1. CO2 enters the bloodstream:
* CO2 produced by cellular respiration in tissues diffuses into the surrounding capillaries.
2. Carbonic Anhydrase (CA) enzyme:
* Red blood cells contain the enzyme carbonic anhydrase (CA).
* CA catalyzes the reversible reaction between CO2 and water (H2O) to form carbonic acid (H2CO3):
CO2 + H2O <=> H2CO3
3. Carbonic Acid Dissociation:
* Carbonic acid is a weak acid and readily dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+):
H2CO3 <=> H+ + HCO3-
4. Bicarbonate Transport:
* Most of the HCO3- diffuses out of the red blood cell into the plasma.
* To maintain electrical neutrality, chloride ions (Cl-) move into the red blood cell (chloride shift).
5. Transport to the Lungs:
* The HCO3- travels in the plasma to the lungs.
6. Reverse Reaction in the Lungs:
* In the lungs, where the partial pressure of oxygen (pO2) is high and the partial pressure of carbon dioxide (pCO2) is low, the reaction reverses:
* H+ and HCO3- recombine to form H2CO3.
* H2CO3 is broken down by CA into CO2 and H2O.
* The CO2 is exhaled.
Summary:
The conversion of CO2 to HCO3- is a crucial process for the transport of CO2 in the blood. It allows for efficient removal of CO2 from the tissues and its subsequent elimination from the body via the lungs.
